A device is known from German Published Patent Application No. 196 23 334 and U.S. Pat. No. 6,148,663 for determining the mass of a medium flowing in a line in which there is a separation opening in a bypass channel. However, in this device, liquid or solid particles present in the medium first flow past the measuring element, and are able to dirty and damage the latter, so as then partially to flow back through the separation opening into the line.
German Published Patent Application No. 198 15 654 shows a device for determining the mass of a medium flowing in a line in which a separation point is present in the bypass channel. The separation point is formed by a separation wall which subdivides the bypass channel into a measuring channel and a return channel.
U.S. Pat. No. 4,914,947 shows a device for determining the mass of a medium flowing in a line, in which contaminants in the flowing medium are pressed against the outer walls by centrifugal forces, and are thus not supposed to reach the measuring channel. In the case of low flow or decreasing (shutting off the internal combustion engine) flow, particularly liquid particles may, on account of gravity, get as far as the input opening of the measuring channel and thus to the measuring element, which they may dirty.
U.S. Pat. No. 3,314,290 shows a bypass channel of a flow meter which subdivides into two exit channels which open back into a line. The exit opening of the exit channels is, however, positioned in such a way that a medium flowing in the bypass channel leaves the exit opening in a direction parallel to the main flow direction in the line.
U.S. Pat. No. 4,887,577 shows a bypass channel of an air flow meter which subdivides at a separation point into two exit channels, a rounded projection being present at the separation point. However, sensors of the air flow meter are situated unprotected in the bypass channel.
U.S. Pat. No. 5,467,648 shows projections at the outer wall of a measuring housing which are situated upstream from lateral exit openings of a bypass channel in the measuring housing. However, sensors of the air flow meter are situated unprotected in the bypass channel.
U.S. Pat. No. 4,403,506 shows an air-mass flow sensor having a wedge-shaped body, which is situated in a flowing medium and which subdivides the medium into two partial flows.